Increasing conjugated linoleic acid (CLA) content of milk fat from lactating dairy cattle has become a research interest due to the possible health benefits afforded humans consuming CLA. Dietary supplementation of CLA to lactating dairy cows is one potential method by which CLA content of milk and dairy products may be enhanced. Feeding CLA in calcium salt form could potentially deliver CLA to the lower digestive tract through prevention of biohydrogenation by rumen microbes. Milk fat depression (MFD) occurs when cows receive CLA-60, a commercially available CLA source containing numerous CLA isomers, abomasally. Our objectives were to determine the quantity of CLA as calcium salts required to elicit maximal MFD and to evaluate the effects of CLA supplementation on fatty acid composition of milk fat. Five Holstein cows at approximately 93 DIM were utilized in a 5 x 5 balanced Latin square crossover design. Periods were 14-d in length with a 5-d treatment phase and 9-d rest phase. Treatments were 5-d supplementation of 0, 12.5, 25, 50, and 100 g of CLA-60 in calcium salt form. Milk samples were collected on d 5 of CLA supplementation and analyzed for composition and fatty acid profile. Regression analysis of milk fat data suggested that MFD was not maximized over the dose levels investigated, despite delivery of 34.5 g of trans-10, cis-12 CLA in the 100-g dose of CLA. Supplementation with 50 and 100 g of CLA per day resulted in a reduction of milk fat percent of 29 and 34%, respectively. Trend analysis indicated a linear decrease in the milk fat content of caprylic, capric, and lauric acids as the dose of CLA increased. Milk fat content of cis-9, trans-11, and trans-10, cis-12 CLA increased at an increasing rate as dose increased.

Intravenous infusion of conjugated linoleic acid (CLA) was evaluated as a simpler method than abomasal infusion and the feeding of calcium salts to examine milk fat depression. The objectives were to determine the dose-dependent response of milk fat and plasma metabolites to intravenous administration of the trans-10, cis-12 isomer of CLA, an isomer identified to possess an inhibitory effect on milk fat synthesis. Four multiparous Holstein cows averaging 123 +/- 30 d in milk were randomly assigned to treatments in a 4 x 4 Latin square design. Catheters were inserted into the jugular vein for infusions and blood sampling. Treatments consisted of intravenous infusions of 0, 2, 4, and 6 g/d CLA (> 95% trans-10, cis-12 CLA). Infusates contained 72 g/d of a parenteral solution, saline, and CLA to 90 ml. Periods were of 5 d duration with a 7 d wash out. Milk was sampled at each milking and analyzed for fat, protein, and fatty acids. Blood samples were obtained on the last day of each period. Dry matter intake (22.4 +/- 2.4 kg/d), milk yield (28.5 +/- 3.3 kg/d), and protein percent (3.26 +/- 0.08%) of cows were not affected by treatment. However, milk fat percentage was reduced linearly with increasing doses of CLA. Milk fat percentage was 4.17, 3.53, 3.29, and 2.92% on d 5 for treatments 0, 2, 4, and 6 g/d CLA, respectively. Concentrations (4.2 mg/g of fat) of cis-9, trans-11 CLA in milk fat were not affected by treatment. However, an increase in the trans-10, cis-12 CLA content of milk fat was observed. Milk fat contained 0.00, 0.02, 0.06, and 0.10 mg of trans-10, cis-12 CLA per g of fat (SEM = 0.065) for treatments 0, 2, 4, and 6 g/d CLA, respectively. Plasma NEFA concentration increased linearly with the dose of the trans-10, cis-12 CLA. Intravenous infusion of the trans-10, cis-12 isomer of CLA depressed milk fat in a linear manner over the range of infusion studied and, therefore, is an alternative to abomasal infusion.